The present invention relates to a communication system by radio connection functioning according to an optimum mode for the consumption of energy and comfort of use.
Communication systems by radio connection, comprising at least one emitter-receiver pair, are most often supplied by a battery. So as to give them autonomy of operation for about 10 years, there is used an intermittent mode of operation for the receivers. Thus, there alternates an active mode, consuming a great deal of energy, with a stand-by mode in which the energy consumption is reduced. Suitable dimensioning of the cyclic ratio between the active mode and the stand-by mode permits achieving a satisfactory mean consumption leading to the desired autonomy.
However, contrary to a receiver continuously in active mode, which is to say always ready to detect a signal, this mode of alternate operation implies that the time of establishing a radio dialogue depends on the instant at which the receiver is in the active mode. Because of this, it is important that the time during which the receiver is in the active mode be sufficient to establish communication.
Thus, at the beginning of all communication by radio connection, the emitter will deliver a field toward the receiver so as to initiate communication. In the course of this emission, the emitter must take account of the fact that the receiver operates in an intermittent manner and that it is therefore only cyclically to receive and during a certain period of time.
However, it has been noted that the systems whose energy consumption has been optimized have a stand-by time much longer than the active time, which results in degrading the comfort of use particularly by prolonging the time for establishing communication.
Thus, EP-A-0 319 219 provides an apparatus for data exchange comprising reception means for radio signals on a predetermined radio channel, means for detection of signals in response to the reception means to detect synchronization signals and means for energy supply to control said means. This apparatus operates in an intermittent manner between an active mode and a stand-by mode, the active mode permitting receiving signals which, subjected to the detection means, permit triggering the establishment of a dialogue. Energy economy is obtained by imposing a stand-by mode as soon as the signal in the transmission is detected or a specific signal is detected and controls the stand-by mode for a predetermined period of time during which no establishment of dialogue can be effected.
As a result, the time in the stand-by mode of the system is favored, so as to save energy by preventing particularly the establishment of a dialogue during predetermined periods of time. Such a system requires therefore defining the ranges of times in which no communication can be established, which limits the comfort of use.
There should accordingly be provided a communication system by radio connection which permits optimum consumption of energy whilst ensuring comfort of use, and particularly by guaranteeing the shortest possible time for establishing the dialogue.